Prevalence and Molecular Genetic Typing of Nonsyndromic Sensorineural Deafness in Chuvash Republic

Summarized genetic epidemiological characteristics of nonsyndromic sensorineural deafness in six raions of Chuvash Republic (Cheboksary, Kanash, Morgaushi, Tsivil'sk, Mariinski Posad, and Alatyr') are presented. A total of 264419 individuals were examined. Forty-five families (60 affected individuals) with autosomal recessive (AR) and 8 families (18 affected individuals) with autosomal dominant (AD) nonsyndromic sensorineural deafness (NSSD) were identified. The load of AD and AR NSSD in the raions examined was estimated. A correlation between the distribution of AR NSSD and genetic drift was demonstrated. Furthermore, the load of AR NSSD was substantially higher in the regions with higher differentiation level. The Spearman's correlation coefficient value was 0.87. Typing of the 35delG mutation in the gene for connexion 26 was carried out in 34 patients from 26 families with AR NSSD. Comparative estimates of the NSSD prevalence in a number of Russian populations were performed.     

Hereditary deafness in Kirov oblast: a genetic epidemiological study

The results of a genetic epidemiological study of hereditary deafness (HD) in ten raions (districts) of Kirov oblast (administrative region), Russia, are presented. A total of 122 075 people have been examined. Segregation analysis of all families with diagnosed HD has demonstrated a good fit to either the autosomal dominant (AD) or autosomal recessive (AR) mode of inheritance. The total prevalence rates of AD and AR HDs, as well as the specific prevalence rates of nonsyndromic and syndromic forms of HD, have been calculated for the population often raions. The HD prevalence rate in Kirov oblast has been found to be 1 : 1043 people (1 : 1453 and 1 : 3699 for the nonsyndromic and syndromic forms, respectively). This value has been found to vary in different raions, which is explained by differences in the genetic subdivision levels of the populations studied; the correlation coefficient between the HD load and random inbreeding (F(ST)) in district populations is r = 0.81 +/- 0.22. The diversity of syndromic hearing disorders is described.     

Hereditary deafness in Kirov oblast: A genetic epidemiological study

The results of a genetic epidemiological study of hereditary deafness (HD) in ten raions (districts) of Kirov oblast (administrative region), Russia, are presented. A total of 122 075 people have been examined. Segregation analysis of all families with diagnosed HD has demonstrated a good fit to either the autosomal dominant (AD) or autosomal recessive (AR) mode of inheritance. The total prevalence rates of AD and AR HDs, as well as the specific prevalence rates of nonsyndromic and syndromic forms of HD, have been calculated for the population of ten raions. The HD prevalence rate in Kirov oblast has been found to be 1: 1043 people (1: 1453 and 1: 3699 for the nonsyndromic and syndromic forms, respectively). This value has been found to vary in different raions, which is explained by differences in the genetic subdivision levels of the populations studied; the correlation coefficient between the HD load and random inbreeding (F _ST) in district populations is r = 0.81 ± 0.22. The diversity of syndromic hearing disorders is described.     

The load and diversity of hereditary diseases in four raions of Rostov oblast

The results of a medical genetic survey of the population of four raions (176535 individuals) of Rostov oblast (Dubovsky, Zimovnikovsky, Myasnikovsky, and Krasnosulinsky raions) are presented. The load of autosomal dominant (AD), autosomal recessive (AR), and X-linked hereditary diseases for urban and rural population was calculated, and the diversity of monogenic hereditary diseases (MHD) was reviewed. The nosological spectrum of MHD constituted 117 diseases (63 diseases with AD inheritance; 38, with AR inheritance; and 16, with X-linked inheritance). The analysis showed that the incidence of MHD among the population of Rostov oblast was 1: 336. Considerable differentiation in the prevalence rates of MHD (AD, AR, and X-linked pathologies) among certain raions was revealed.     

A medico-genetic description of inhabitants of two regions of the Kransnodar Krai]

The spectrum and prevalence rate of hereditary pathology in Kanevskii and Bryukhovetskii raions (districts) of Krasnodar krai (territory) were analyzed. The total size of the studied population was 145,937. The prevalence rate of monogenic hereditary pathology was estimated. This value was 1.08 +/- 0.08, 0.72 +/- 0.07, and 0.20 +/- 0.06 per 1000 people for autosomal dominant (AD), autosomal recessive (AR), and X-linked (XL) recessive diseases, respectively. Forty-two AD (158 affected persons in 82 families), 32 AR (105 affected persons in 82 families), and 6 XL disease entities (13 affected persons in 8 families) were found. A slight genetic subdivision was found in the populations of Kanevskii and Bryukhovetskii raions. However, it was not found to affect the prevalence of hereditary pathology.     

Contribution of DFNB1 and DFNB2 loci to neurosensory deafness in affected Tunisian families

Classical studies have demonstrated genetic heterogeneity for nonsyndromic autosomal recessive congenital neurosensory deafness. The first two DFNB1 and DFNB2 locations were found using two consanguineous Tunisian families respectively from north and south. We tested these loci for cosegregation with deafness in twenty four southern families with nonsyndromic presumed congenital sensorineural deafness and a pedigree structure consistent with autosomal recessive inheritance. Only in our families, did deafness cosegregate with DFNB1. Although our families are from the south, none of them showed linkage to DFNB2.     

Epidemiology of monogenic hereditary diseases in Rostov oblast: Population dynamic factors determining the differentiation of the load of hereditary diseases in eight districts

A genetic epidemiological study has been carried out in eight raions (districts) of Rostov oblast (region) of Russia: Tsimlyansk, Volgodonskoi, Tselina, Egorlykskaya, Millerovo, Tarasovskaya, Rodionovo-Nesvetaiskaya, and Matveevo-Kurgan raions. The population structure (the parameters of the isolation by distance model, ethnic assortative marriage, random inbreeding (F _ST), endogamy index, and ie) and the genetic demographic characteristics of the regional population (vital statistics, Crow’s index, and its components) have been analyzed. The total sample size was 320 925 subjects (including 114 106 and 206 816 urban and rural residents, respectively). The load of the main types of Mendelian diseases (autosomal dominant (AD), autosomal recessive (AR), and X-linked diseases) has been calculated for the total sample from eight districts and separately for the urban and rural populations. Substantial differences between individual districts in the AD and AR genetic loads have been found, especially upon separation into urban and rural samples. The results of correlation analysis suggest that migration and genetic drift are the main factors of genetic differentiation of populations with respect to the prevalence of hereditary diseases.     

Genetic Epidemiological Study of Three District Populations in Chuvashia

Comprehensive population genetic and medical genetic studies were performed in three raions (districts) of Chuvashia. The population of these districts is more than 90% Chuvash. About 70% of the families that completed reproduction had two or three children. The proportion of families with four or more children was 18%. The duration of generation was 27.6 years. The differential fertility and differential mortality indices in the Chuvash population were estimated at 0.33 and 0.076, respectively. The total index of differential selection was 0.403, which is typical of modern urbanized populations. Mean values of local inbreeding calculated from Malecot's model of isolation by distance were 0.00124 and 0.00377 for the urban and rural populations, respectively, of the districts studied. The prevalence rates of autosomal dominant (AD), autosomal recessive (AR), and X-linked diseases were found to be 0.47, 0.52, and 0.35 per 1000, respectively, in the urban population and 1.62, 1.14, and 0.31 per 1000, respectively, in the rural population. Significant correlation between the local inbreeding and prevalence rates of AD and AR diseases was found. A total of 43 AD and 43 AR diseases were identified. Some of them were not found in previous studies on other populations.     

Genetic epidemiological study of populations in three regions of Chuvashia Republic

Comprehensive population genetic and medical genetic studies were performed in three raions (districts) of Chuvashia. The population of these districts is more than 90% Chuvash. About 70% of the families that completed reproduction had two or three children. The proportion of families with four or more children was 18%. The duration of generation was 27.6 years. The differential fertility and differential mortality indices in the Chuvash population were estimated at 0.33 and 0.076, respectively. The total index of differential selection was 0.403, which is typical of modern urbanized populations. Mean values of local inbreeding calculated from Malecot's model of isolation by distance were 0.00124 and 0.00377 for the urban and rural populations, respectively, of the districts studied. The prevalence rates of autosomal dominant (AD), autosomal recessive (AR), and X-linked diseases were found to be 0.47, 0.52, and 0.35 per 1000, respectively, in the urban population and 1.62, 1.14, and 0.31 per 1000, respectively, in the rural population. Significant correlation between the local inbreeding and prevalence rates of AD and AR diseases was found. A total of 43 AD and 43 AR diseases were identified. Some of them were not found in previous studies on other populations.     

The contribution of the DFNB1 locus to neurosensory deafness in a Caucasian population.

Classical studies have demonstrated genetic heterogeneity for nonsyndromic autosomal recessive congenital neurosensory deafness, with at least six loci postulated. Linkage analysis in two consanguineous Tunisian kindreds has demonstrated that one such deafness locus, DFNB1, maps near chromosome 13 markers D13S175, D13S143, and D13S115. We tested these markers for cosegregation with deafness in 18 New Zealand and 1 Australian nonconsanguineous kindreds, each of which included at least two siblings with nonsyndromic presumed congenital sensorineural deafness and that had a pedigree structure consistent with autosomal recessive inheritance. When all families were combined, a peak two-point lod score of 2.547 (theta = .1) was obtained for D13S175, 0.780 (theta = .2) for D13S143, and 0.664 (theta = .3) for D13S115. While there was no statistically significant evidence for heterogeneity at any of the three loci tested, nine families showed cosegregation of marker haplotypes with deafness. These observations suggest that the DFNB1 locus may make an important contribution to autosomal recessive neurosensory deafness in a Caucasian population. In the nine cosegregating families, phenotypic variation was observed both within sibships (in four families), which indicates that variable expressivity characterizes some genotypes at the DFNB1 locus, and between generations (in two families), which suggests allelic heterogeneity.     

Genetic structure of the Udmurt population

Integrated study of the genetic structure of the Udmurt population with respect to different genetic systems has been performed. Data on the genes of genetic diseases, abiotic parameters analyzed by population statistic methods, and DNA polymorphism are summarized. The populations of six raions (districts) of Udmurt Republic (the Mozhga, Malaya Purga, Sharkan, Debesy, Igra, and Glazov raions) have been studied. The total population studied was 267 655 people (an urban population of 150 119 people and a rural population of 117 536 people), including 155 346 Udmurts. The population structure has been studied in six districts on the basis of the vital statistics, Crow’s indices, Malecot’s isolation by distance parameters, ethnically assortative marriage parameters, endogamy indices, inbreeding-endogamy (ie) indices, and frequencies of the genotype and allele frequencies of four DNA markers (17 alleles). The prevalences of hereditary diseases have been calculated for different population groups: urban and rural populations, Udmurts and other ethnic groups. These groups, especially the urban and rural populations, substantially differed from one another in the prevalences of autosomal dominant (AD) and autosomal recessive (AR) diseases. The correlation between the prevalence of AD and AR diseases and the ie index is positive and significant. The spectrum of hereditary diseases detected in six districts of Udmurtia comprises 149 diseases (80, 57, and 12 AD, AR, and X-linked diseases, respectively). Accumulation of individual diseases in districts of Udmurtia and accumulation of diseases in Udmurtia as compared to regions studied earlier has been found. Cluster analysis of the frequencies of genes of AD and AR diseases and DNA markers has determined the gene geographic position of Udmurts.     

Genetic structure of the Udmurt population

Integrated study of the genetic structure of the Udmurt population with respect to different genetic systems has been performed. Data on the genes of genetic diseases, abiotic parameters analyzed by population statistic methods, and DNA polymorphism are summarized. The populations of six raions (districts) of Udmurt Republic (the Mozhga, Malaya Purga, Sharkan, Debesy, Igra, and Glazov raions) have been studied. The total population studied was 267,655 people (an urban population of 150,119 people and a rural population of 117,536 people), including 155,346 Udmurts. The population structure has been studied in six districts on the basis of the vital statistics, Crow's indices, Malecot's isolation by distance parameters, ethnically assortative marriage parameters, endogamy indices, inbreeding-endogamy (ie) indices, and frequencies of the genotype and allele frequencies of four DNA markers (17 alleles). The prevalences of hereditary diseases have been calculated for different population groups: urban and rural populations, Udmurts and other ethnic groups. These groups, especially the urban and rural populations, substantially differed from one another in the prevalences of autosomal dominant (AR) and autosomal recessive (AR) diseases. The correlation between the prevalence of AD and AR diseases and the ie index is positive and significant. The spectrum of hereditary diseases detected in six districts of Udmurtia comprises 149 diseases (80, 57, and 12 AD, AR, and X-linked diseases, respectively). Accumulation of individual diseases in districts of Udmurtia and accumulation of diseases in Udmurtia as compared to regions studied earlier has been found. Cluster analysis of the frequencies of genes of AD and AR diseases and DNA markers has determined the gene geographic position of Udmurts.     

Diversity and Prevalence of Hereditary Diseases among Nogais of the Karachay-Cherkess Republic

The diversity and prevalence of hereditary diseases (HDs) among Nogais of the Karachay-Cherkess Republic (KChR) are described. The size of the surveyed KChR population was 387231 individuals, including 3.81% Nogais (14741 individuals). We revealed 36 nosological forms of HDs (110 patients from 81 families): 22 with autosomal dominant (AD) inheritance, 10 with autosomal recessive (AR) inheritance, and 4 with X-linked inheritance. The prevalence of HDs in Nogais was 1: 134. The features of HD diversity in Nogais were determined in comparison with the previously surveyed populations of Russia. The accumulation of Ehlers–Danlos syndrome (1: 388), AD amelogenesis imperfecta (1: 3685), AD ichthyosis (1: 4914), AR nonsyndromic mental retardation (1: 1340), AR Gilbert syndrome (1: 4914), and X-linked inherited deficit of glucose-6-dehydrogenase (1: 1774 males) was established. The analysis of heterozygous carriage of mutations “major” for Russia in the genes of the four following AR diseases in 118 unrelated clinically healthy Nogais (236 analyzed chromosomes) was performed: cystic fibrosis (13 mutations in the CFTR gene: CFTRdele2,3 (21 kb), F508del, I507del, 1677delTA, 2184insA, 2143delT, 2183AA>G, 2184delA, 394delTT, 3821delT, L138ins, E92K, W1282X); phenylketonuria (six frequent mutations in the PAH gene: R261X, R408W, R413P, F331S, P211T, P211L); nonsyndromic sensorineural hearing loss (35delG mutation in the GJB2 gene); and Gilbert syndrome (an increase in the number of TA repeats in the UGT1A1 gene). Allelic specificity for all studied genes in the Nogai people was revealed.     

Localization of a novel autosomal recessive non-syndromic hearing impairment locus (DFNB38) to 6q26-q27 in a consanguineous kindred from Pakistan

For autosomal recessive nonsyndromic hearing impairment over 30 loci have been mapped and 19 genes have been identified. DFNB38, a novel locus for autosomal recessive nonsyndromic hearing impairment, was localized in a consanguineous Pakistani kindred to 6q26-q27. The affected family members present with profound prelingual sensorineural hearing impairment and use sign language for communications. Linkage was established to microsatellite markers located on chromosome 6q26-q27 (Multipoint lod score 3.6). The genetic region for DFNB38 spans 10.1 cM according to the Marshfield genetic map and is bounded by markers D6S980 and D6S1719. This genetic region corresponds to 3.4 MB on the sequence-based physical map.     

Novel mutations in the connexin 26 gene (GJB2) that cause autosomal recessive (DFNB1) hearing loss.

Mutations in the connexin 26 (Cx26) gene (GJB2) are associated with the type of autosomal recessive nonsyndromic neurosensory deafness known as "DFNB1." Studies indicate that DFNB1 (13q11-12) causes 20% of all childhood deafness and may have a carrier rate as high as 2. 8%. This study describes the analysis of 58 multiplex families each having at least two affected children diagnosed with autosomal recessive nonsyndromic deafness. Twenty of the 58 families were observed to have mutations in both alleles of Cx26. Thirty-three of 116 chromosomes contained a 30delG allele, for a frequency of .284. This mutation was observed in 2 of 192 control chromosomes, for an estimated gene frequency of .01+/-.007. The homozygous frequency of the 30delG allele is then estimated at .0001, or 1/10,000. Given that the frequency of all childhood hearing impairment is 1/1,000 and that half of that is genetic, the specific mutation 30delG is responsible for 10% of all childhood hearing loss and for 20% of all childhood hereditary hearing loss. Six novel mutations were also observed in the affected population. The deletions detected cause frameshifts that would severely disrupt the protein structure. Three novel missense mutations, Val84Met, Val95Met, and Ser113Pro, were observed. The missense mutation 101T-->C has been reported to be a dominant allele of DFNA3, a dominant nonsyndromic hearing loss. Data further supporting the finding that this mutation does not cause dominant hearing loss are presented. This allele was found in a recessive family segregating independently from the hearing-loss phenotype and in 3 of 192 control chromosomes. These results indicate that 101T-->C is not sufficient to cause hearing loss.     

Analysis of two Arab families reveals additional support for a DFNB2 nonsyndromic phenotype of MYO7A

Variants in the head and tail domains of the MYO7A gene, encoding myosin VIIA, cause Usher syndrome type 1B (USH1B) and nonsyndromic deafness (DFNB2, DFNA11). In order to identify the genetic defect(s) underling profound deafness in two consanguineous Arab families living in UAE, we have sequenced a panel of 19 genes involved in Usher syndrome and nonsyndromic deafness in the index cases of the two families. This analysis revealed a novel homozygous insertion of AG (c.1952_1953insAG/p.C652fsX11) in exon 17 of the MYO7A gene in an Iraqi family, and a homozygous point mutation (c.5660C>T/p.P1887L) in exon 41 affecting the same gene in a large Palestinian family. Moreover, some individuals from the Palestinian family also harbored a novel heterozygous truncating variant (c.1267C>T/p.R423X) in the DFNB31 gene, which is involved in autosomal recessive nonsyndromic deafness type DFNB31 and Usher syndrome type II. Assuming an autosomal recessive mode of inheritance in the two inbred families, we conclude that the homozygous variants in the MYO7A gene are the disease-causing mutations in these families. Furthermore, given the absence of retinal disease in all affected patients examined, particularly a 28 year old patient, suggests that at least one family may segregate a DFNB2 presentation rather than USH1B. This finding further supports the premise that the MYO7A gene is responsible for two distinct diseases and gives evidence that the p.P1887L mutation in a homozygous state may be responsible for nonsyndromic hearing loss.     

Integrated population genetic and medical genetic study of two raions of the Tver oblast

An integrated medical genetic an population genetic study has been performed in two raions (administrative districts) of the Tver oblast (region) of Russia: the Udomlya raion located in the zone affected by the Kalininskaya Nuclear Power Plant and the Ostashkov raion, which served as a control district. No significant differences has been found with respect to the genetic parameters studied. The values of these parameters in the populations of the town of Udomlya, the town of Ostashkov, the Udomlya raion, and the Ostashkov raion, respectively, are the following: random inbreeding, 0.00006, 0.00011, 0.000167, and 0.000366; endogamy index, 0.05, 0.43, 0.30, and 0.42; local inbreeding, 0.0003, 0.00045, 0.0009, and 0.0011; the degree of isolation by distance, 0.0003, 0.00045, 0.0009, and 0.0005; sigma, 2098, 1338, 1473, and 1189; the load of autosomal dominant (AD) diseases, 0.71, 0.92, 0.92, and 1.37; the load of autosomal recessive (AR) diseases, 0.68, 0.69, 0.67, and 0.82; and the load of X-linked diseases, 0.18, 0.64, 0.83, and 0.27.     

Analysis of diversity of autosomal-recessive diseases in Russian populations]

The diversity of autosomal recessive (AR) diseases was studied in six Russian regions: the Kirov, Kostroma, and Bryansk oblasts; Adygea Republic; Krasnodar krai, and Marii El Republic (in the latter region, the Mari and Russian ethnic groups were studied separately). In total, more than 1.5 million people were studied. The spectrum of the AR diseases included 101 nosological forms; the total number of the affected subjects was 942. For all diseases, the prevalence rate in the region where they were found and the mean prevalence rate in the total population studied were calculated. Only seven AR diseases had prevalence rates of 1:50,000 or higher; however, this group contained about 50% of the patients. About half of the AR diseases (66) had an extremely low prevalence rate (1:877,483). Eleven diseases exhibit local accumulation. Accumulation of some or other diseases was only observed in four out of seven populations studied (Marii El, Adygea, and the Kirov and Bryansk oblasts). To determine the cause of the local accumulation of some diseases in populations, correlation analysis of the dependence of accumulation of hereditary diseases on the genetic structure of the populations studied was performed. The accumulation coefficients for AR and autosomal dominant (AD) diseases and the mean values of random inbreeding (Fst) in individual districts were calculated for all populations studied. The coefficients of the Spearman rank correlation between the accumulation coefficient and random inbreeding (Fst) were 0.68 and 0.86 for the AD and AR diseases, respectively. The correlation between the accumulation of AD and AR diseases was 0.86. The relationships found indicate that the diversity of AD and AR diseases, as well as the genetic load, distinctly depended on the population genetic structure and were largely determined by genetic drift.     

Population genetics of hereditary diseases in the child population of the Republic of Bashkortostan, Chuvashia, and Udmurtia

The results of integrated study of the genetic structure and prevalence of monogenic hereditary diseases (MHDs) in the child population of three republics of Russia are summarized. Eight raions (districts) of the Republic of Bashkortostan and six districts of each Republic of Chuvashia and Republic of Udmurtia has been surveyed. The total population surveyed was 782184 people, with children accounting for 24.67% of them (192992 children). The loads of autosomal dominant (AD), autosomal recessive (AR), and X-linked MHDs have been calculated separately for urban and rural populations; differences between individual populations in the MHD load have been found. The differentiation of subpopulations with respect to MHD prevalence is explained by differences in the degree of subdivision. The MHD spectrum in the child population of the three republics comprises 222 disease entities, including 121 AD, 83 AR, and 18 X-linked diseases. Group of highly prevalent MHDs in regional child populations have been determined. The mean fitness of MHD patients in Bashkortostan has been calculated; it is 0.87, 0.04 and 0.16 for AD, AR, and X-linked diseases, respectively. Analysis has demonstrated that the prevalence rates of MHDs in the child populations of the republics of Chuvashia, Udmurtia, and Bashkortostan are 1, 1.2, and 1.4%, respectively.